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ORA-12203: TNS:unable to connect to destination

Recently, we've suddenly starting getting this error message when users are trying to connect to our production database from remote clients. However, by the time we are notified we can login without any problems. It is very hard to diagnose this error as we cannot reproduce it. Occasionally, this occurs (several times per week) and is causing production jobs to fail (they have to restarted and usually they are fine). We are using ONames and Oracle8i on Solaris. Has anyone encountered a similar situation and any recommendations?
Thanks.

My initial (help desk educated) gut feeling tells me this is a networking issue. Try pinging the server the next time this happens and see if it times out intermittantly. Net-Op into one of the problem workstations and ping the server from there.

Aside from that, did you check your alert.log, is the listener going down?

Alert.log does not show any errors. Listener is not going down. The only other thing is the sqlnet.log shows TNS-12547 and TNS-12537. This error occurs for such a small period of time that by the time we notice it it no longer is a problem.

Originally posted by axe Alert.log does not show any errors. Listener is not going down. The only other thing is the sqlnet.log shows TNS-12547 and TNS-12537. This error occurs for such a small period of time that by the time we notice it it no longer is a problem.

Look in the sqlnet.ora and the listener.ora for a timeout parameter. If there is a timeout parameter you may want to either increase the number or set it to 0 for infinite. It could be that from time to time there is an increase in network latency If Oracle doesn't wait long enough it might give you that error message. Just a thought.

Can you stay logged in via your SQL session?
If you can, than this adds to my initial theory that it is a network glitch.

I had a DB that had users based at a remote location and they had the same problem, this was due to network problems at the site. When I logged in from my W/S there were no problems. So, as much as they say it is, it is NOT always an Oracle problem.

Alert.log does not show any errors. Listener is not going down. The only other thing is the sqlnet.log shows TNS-12547 and TNS-12537. This error occurs for such a small period of time that by the time we notice it it no longer is a problem.